fly the flag
verb1
To be registered in a particular country and display that country's flag as a result. (of a ship, airline etc)
2
Idiomatic To support one's country enthusiastically.
- Now they are the English champions, flying the flag for their country in Europe’s premier club competition and managed by a 53‑year‑old who only got the job on Sunday night.2017 March 14, Stuart James, “Leicester stun Sevilla to reach last eight after Kasper Schmeichel save”, in the Guardian: